The personal computer industry has grown enormously in the past decade and has created a large market in software suitable for operation of personal computers. Many companies are in the business of creating and publishing computer software packages which are then marketed to personal computer owners for use in their machines. Typically such computer software packages are marketed on a fixed fee basis in which a user purchases a copy of the software, usually under terms of a written license, for a fixed price thereby granting to the user perpetual use of the software. It has been a characteristic of this industry that in order for the publishers of the software to recover the often quite large investment in research and development of the software, and also the costs of manufacture and marketing, that the purchase price of many such software items has been relatively high, particularly for limited distribution or special-purpose software. This high purchase price has been a barrier, in some circumstances, to the widespread sale of some software and has limited the penetration of software publishers in some markets. In addition, some users are reluctant to incur such a purchase price without first operating the software, since the suitability of software is very difficult to judge without actually using it.
The relatively high purchase price of software has lead to another phenomenon perceived as a problem by many software publishers. It is often relatively easy for a personal computer owner to make duplicate copies of any software which the owner has purchased unless the software is in some fashion protected from such copying. It has become quite common for some personal computer owners to make and disseminate such copies to their friends and acquaintances. This often widespread unauthorized copying dilutes the market for the software product and may cause the publisher to ask even a higher price for each legitimate copy of the product in order to ensure a reasonable amount of return.
One solution to this dilemma has been for manufacturers to institute copy protection schemes which are intended to allow media carrying personal computer software to be sold with the media containing technical devices intended to ensure that unauthorized copies cannot be made on personal computers. Copy protection schemes were put into place by a variety of companies using various techniques. One technique was to use a non-standard format for the magnetic disk on which the program was stored, with the non-standard format not being copyable given the operating system for the personal computer for which the program was intended. A second technique which was used was to introduce limited format error or an altered physical characterisfic into the disk which the computer is unable to duplicate when copying the disk. Special commands in the program would then check for that identifying information before allowing operation of any programs on the disk and thus to ensure that the disk was not a copy. It has been a more recent trend that a third category of software protection schemes have been proposed which involve physical protection either by making physical variances in the disk which must be checked by the program before it can operate or by requiring hardware devices, known as "locks," which must be purchased along with the software in order to operate it. All such copy protection schemes have suffered from some disadvantages in that the technique of protection of many of the schemes have been deduced by individual computer owners who then widely publish how the copying protection scheme may be avoided. Certain programs are also sold commercially which enable the copying of certain disks which are otherwise intended to be copy protected. Hardware based systems can also be avoided by the custom creation of hardware devices which can emulate the lock intended to be sold with the system.
It is also generally known in the prior art that computer programs can be encrypted or encoded so that they must be used with a special microprocessor or other unique hardware having the capacity to decrypt or decode the program. Such systems are limited to the particular encryption/decryption system hard-wired into the computer and thus are vulnerable to unauthorized use once the methodology of the system is deduced once by a user.